U.S. Pat. No. 4,454,064 discloses a method for preparing pentaerythritol phosphate alcohol, which comprises reacting pentaerythritol and POCl3 in dioxane solvent at 75-125xc2x0 C. The pentaerythritol phosphate alcohol prepared is an intermediate that can be used to synthesize PU flame retardants and plasticizers. HCl gas is also generated in this method, and a large amount of water is required to wash away HCl from the product mixture. Moreover, an excessive amount of POCl3 is used in this method, which results in a residue solution containing unreacted POCl3.
U.S. Pat. No. 4,478,998 (1984) discloses a method for synthesizing amino-s-triazine salt of a phosphoric acid from pentaerythritol phosphate alcohol. The amino salt synthesized can be used as a flame retardant additive for special polymeric compositions.
The present invention provides a waste-reduction process for producing pentaerythritol phosphate alcohol. The features of the process of the present invention are as follows:
1. The process uses P2O5 as a reactant.
2. The process uses a mechanochemical synthesis method and uses a ball mill as a reactor.
3. The process uses an alkyl benzene, such as toluene or xylene, as a solvent. The alkyl benzene may have one or two identical or different alkyls having 1 to 5 carbons.
4. The solvent used in the process is pre-heated to 70-150xc2x0 C.
5. The process uses metal halide MX2, such as MgCl2 etc., as a catalyst, wherein M=Mg, Zn, or Al; and X=Cl, or Br. The weight ratio of the catalyst to pentaerythritol is 1:99 to 5:95.
Compared to the conventional process, a waste-reduction process for producing pentaerythritol phosphate alcohol according to the present invention has the following three advantages: (a) no generation of waste gas of HCl; (b) free of a waste aqueous solution generated from neutralization of HCl waste gas; and (c) avoiding handling of a residue solution containing unreacted POCl3. Since the present invention uses P2O5 to replace POCl3, no HCl is generated in the process, and no residue solution containing unreacted POCl3 is formed. Moreover, the solvent used in the present invention (e.g. toluene) can be recycled, thereby achieving an objective of waste reduction.
Pentaerythritol will become a molten state in toluene at 90-100xc2x0 C. and can react with P2O5. Since a molten pentaerythritol has a very high viscosity and is difficult to be agitated, the reaction yield is usually not high. Therefore, a mechanochemical synthesis, e.g. a ball mill, is used to achieve an ideal agitatioin such that pentaerythritol and P2O5 can have a sufficient contact with each other, thereby increasing the yield. The present invention adopts a ball mill process which also achieves the following improvements: increasing the purity, increasing the yield, reducing the particle size, simplifying the process, and without heating/cooling during the reaction.